1. Field of the Invention
The present invention relates to a method and an apparatus for measuring the quantum efficiency, and an integrator directed thereto.
2. Description of the Background Art
In recent years, development of fluorescent lamp and display has been advancing rapidly. With such development, the quantum efficiency has become of interest as an indicator for more accurately evaluating the performance of a phosphor used for the lamp and display. In general, the quantum efficiency refers to the ratio of the number of photons generated from a sample (typically phosphor) to the number of photons absorbed by the sample.
For example, Ohkubo and Shigeta, “Absolute Fluorescent Quantum Efficiency of NBS Phosphor Standard Samples,” Journal of the Illuminating Engineering Institute of Japan, The Illuminating Engineering Institute of Japan, 1999, Vol. 83, No. 2, pp. 87-93, discloses a typical configuration for measuring the quantum efficiency. Instead of such a typical configuration, Japanese Patent Laying-Open Nos. 09-292281, 10-142152, and 10-293063 for example each disclose an alternative configuration for measuring the quantum efficiency.
The configuration for measuring the quantum efficiency as described above is adapted chiefly to measurement of the quantum efficiency of a solid sample, or a sample molded in the form of a solid. Specifically, the quantum efficiency of the sample is measured by applying excitation light to the sample and acquiring fluorescence emitted from the sample.
For example, phosphors used for EL (Electro Luminescent) emission are powder phosphors in many cases. In such cases, a powder sample is dissolved in a solvent and the quantum efficiency of the sample in the form of the solution is measured. For measurement of the quantum efficiency of such a solution, the solution sample is enclosed in a translucent container, and then excitation light is applied to the solution sample in the container to cause fluorescence to be generated.
Such a measurement system, however, may involve a problem of measurement errors due to re-excitation (secondary excitation). Specifically, a phenomenon may occur in which the excitation light after having passed through the solution sample is reflected from the interior of an integrating sphere or the like and then enters again the solution sample, resulting in emission of fluorescence of an amount larger than that which should otherwise be emitted.